Method and device for transferring a pattern

ABSTRACT

A method and a device for transferring a pattern in the form of a structure from a pressing means to a layer on a substrate. The layer is heated by a current being supplied through the pressing means in contact with the layer.

FIELD OF THE INVENTION

The present invention relates to a method and a device for heating asubstrate when transferring a pattern from a stamp to a substrate bypressing. More specifically, it relates to a method and a device inconnection with so-called nanoimprint lithography or hot embossing.

BACKGROUND ART

The present application relates to lithography by pressing a stamp witha pattern into a deformable film on a substrate. To allow pressing ofthe pattern from the stamp into the film, the film has to besufficiently soft. This is usually achieved by heating the film so as tomake it soft. This has previously been done, for instance, by heatingthe substrate from one of its sides by means of a hot plate. One problemof this technique is that the heating is not homogeneous. This problemis particularly important in connection with so-called nanoimprintlithography in which the structures which are to be transferred are inthe order of nanometers.

PCT application WO 01/63361 discloses a method and a device forhomogeneous heating of a substrate. This is achieved by providing aheat-absorbing layer, which is arranged so that a homogeneous thermaldistribution is obtained in the layer. The heat is subsequentlytransferred to the substrate.

When heating a substrate in the above manner, a homogeneous heating isobtained over the surface of the substrate. Nevertheless one side of thesubstrate is heated faster than the other, which may result in thesubstrate bending.

If the pattern has to be transferred from the stamp to the substratewith a high degree of accuracy, it is desirable to avoid bending of thesubstrate. Consequently, there is a need for a method and a device whichin a more homogeneous manner heat a layer on a substrate whentransferring a pattern from a stamp to the layer.

SUMMARY OF THE INVENTION

The present invention is intended to provide a method and a device whichovercome at least one of the problems identified above.

An object of the present invention is to provide a method fortransferring a pattern from a stamp to a layer on a substrate bypressing, the layer being heated homogeneously.

It is also an object of the present invention to provide a method fortransferring a pattern from a stamp to a layer on a substrate bypressing, the layer being heated in a fast and controllable manner.

A further object of the present invention is to provide a device fortransferring a pattern from a stamp to a layer on a substrate bypressing, the layer being heated homogeneously.

One more object of the present invention is to provide a device fortransferring a pattern from a stamp to a layer on a substrate bypressing, the layer being heated in a fast and controllable manner.

At least one of these objects is achieved by a method or a deviceaccording to the independent claims.

Further advantages of the invention are stated in the dependent claims.

According to the invention, a method for transferring at least onepattern in the form of a structure from a pressing means to a substrate,which is coated with a layer on at least one planar surface, ischaracterized in that it comprises the following steps: connecting apower source over the pressing means, operating the power source so thata current is passed through the pressing means and heats the pressingmeans and the layer, which is in contact with the pressing means,arranging the pressing means, which has a surface with a structure thatdefines the pattern, said pattern facing the layer, and pressing thepressing means against the layer so that the pattern is transferred tothe layer.

Since the pressing means is heated by a current being passedtherethrough, a considerably more homogeneous heating of the pressingmeans and the layer is allowed, as compared to prior art technique. Themethod according to the invention is particularly useful in so-callednanoimprint lithography in which the size of the structures which are tobe transferred is in the order of nanometers.

Naturally, in a method according to the invention the pressing means hasto be electrically conducting.

According to one embodiment of the invention, the power source isconnected so as to render the current density in the pressing meanshomogeneous. This can be achieved in a number of ways. The power sourcebeing connected in this manner and considering the shape of the pressingmeans, it is possible to connect the pressing means in a suitablemanner. If the pressing means is rectangular, the power source can beconnected along a pair of opposed sides, the power source beingconnected along the entire side of each one of the opposed sides.

If the resistivity increases as the temperature rises, the substratewill be heated in a self-regulating manner. It is thus advantageous tomake the pressing means of a material which has a resistivity thatincreases as the temperature rises.

According to an alternative embodiment, the method further comprises thestep of providing a pressing means which is formed so that the currentdensity in the pressing means will be homogeneous. If the pressing meanshas the shape of a trapezoid, the pressing means is suitably formed soas to be thickest at the end which is closest to the shortest side ofthe two parallel sides of the trapezoid. The pressing means is connectedto the power source along the entirety of the two parallel sides.

If the pressing means has an outer periphery and a hole which defines aninner periphery, the power source is advantageously connected betweenthe inner periphery and the outer periphery.

If a homogeneous current density in the substrate is desirable, thesubstrate is made thicker at the inner periphery. It is particularlyadvantageous to have a circular symmetrical pressing means.

Naturally, it is possible to connect the connecting means in a number ofways, also when the pressing means is circular-symmetrical with an innerand an outer periphery. According to one embodiment, the power source isconnected with the aid of two connecting means, which each extend in theradial direction of the pressing means.

In some cases, it may be difficult to provide a homogeneous currentdensity when the pressing means is irregular in shape. According to oneembodiment of the invention, the step of connecting the pressing meansto a power source comprises the steps of arranging the substrate in arecess in an electrically conducting holder means with a rectangularouter shape, and connecting the holder means to the power source, thepressing means having electrical contact along it entire periphery, andthe combination of holder means and pressing means having the sameelectrical properties as a rectangular plate. In this manner, it isrelatively easy to provide a homogeneous current density in the pressingmeans.

According to one aspect of the invention, a device is provided fortransferring at least one pattern from a pressing means with a structureto a plate shaped substrate, which is coated with a layer on a planarsurface, comprising a first holder means for receiving the substrate, asecond holder means for receiving the pressing means, the device beingarranged to apply a pressure between the first holder means and thesecond holder means. The device is characterized in that it furthercomprises a power source for heating the pressing means, and electricalconnecting means for connecting the pressing means to the power source.

According to one embodiment of the invention, the first holder meanscomprises a rectangular portion with a recess which is formed to receivethe pressing means, which portion is connected on two opposed sides tothe electrical connecting means and has the same resistivity as thesubstrate and which portion together with the pressing means forms aunit with the same electrical properties as a rectangular plate withouta recess.

As a result, it is relatively easy to provide a homogeneous currentdensity in the substrate.

To avoid thermal strain in the pressing means, the pressing means,according to tone embodiment, is resiliently connected to the powersource. According to an alternative embodiment, the pressing means is inmoving contact with the connecting means to enable the pressing means toslide in relation to the connecting means.

It goes without saying that the different features of the device can becombined with each other in the same way as the different features ofthe method can be combined with each other. Furthermore, the, differentfeatures of the device are applicable to the method and vice versa.

Below various embodiments of the invention will be described withreference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a method according to the invention.

FIG. 2 shows a pressing means with connecting means according to anembodiment, of the invention.

FIG. 3 shows a pressing means arranged in a portion according to analternative embodiment of the present invention.

FIG. 4 shows a pressing means according to an alternative embodiment ofthe present invention.

FIG. 5 shows a device according to an embodiment of the invention.

FIG. 6 shows two different embodiments for connection of connectingmeans to the pressing means.

FIG. 7 shows a further embodiment for connection of connecting means toa pressing means.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

FIG. 1 illustrates a method according to the invention. A pressing means1 is arranged on a first holder means 2. The pressing means 1 isprovided with a pattern 3 in the form of raised portions on one of itssides. The pattern 3 is facing a layer 4 which is arranged on asubstrate 5. The substrate 5 is arranged on a second holder means 6. Afirst connecting means 7 and a second connecting means 8 are arranged onone side each of the substrate 5.

When the pattern 3 is to be transferred from the pressing means to thelayer, it is necessary to first heat the layer 4 to make, it deformable.For this purpose, a voltage is applied over the connecting means so thata current is passed through the pressing means after the pressing meanshas been brought into contact with the layer. The connecting means 7, 8are designed so that the current through the pressing means will have ahomogeneous density. The current through the pressing means causes it tobe heated and the layer to soften. By measuring the resistance betweenthe connecting means, it is possible to control the temperature so as toattain the desirable temperature.

When the layer is heated to the desirable temperature, a pressure isapplied between the first holder means 2 and the second holder means 6,whereby the pattern is transferred to the layer 4.

FIG. 2 a shows a rectangular pressing means 10 with a first connectingmeans 11 and a second connecting means 12 arranged on one side each ofthe pressing means 10. Each of the connecting means is in contact withthe pressing means along the entire side of one of the sides of thepressing means, thereby ensuring a homogeneous current density in thepressing means. FIG. 2 b is a cross-sectional view of the pressingmeans.

FIG. 3 shows how a first connecting means 13 and a second connectingmeans 14 are arranged on a portion 15 in which the pressing means 16 isprovided. The pressing means 16 is circular and arranged in a circularrecess in the portion 15 with electrical contact between the pressingmeans and the connecting means along the entire periphery of thepressing means. The portion is made of the same material as the pressingmeans, which makes the current distribution between the connecting meansessentially the same as in the embodiment shown in FIG. 2.

FIG. 4 shows a circular pressing means 17 which is defined by an outerperiphery 18 and an inner periphery 19 which defines a circular throughhole. When a voltage is applied between the inner and the outerperiphery, the current is passed radially through the pressing means.The pressing means 17 is thicker towards the center in such manner thatthe current density will be constant, which results in a homogeneousheating of the pressing means and thus also of the layer. As analternative, the pressing means is formed so that a desirable radialtemperature distribution is obtained. Connecting means 40, 41 areconnected, respectively, at the inner and the outer periphery of thepressing means.

FIG. 5 schematically shows a device for transferring a pattern from apressing means 20 to a layer 21 on a substrate 22. The device comprisesa power unit 23 which is connected to both sides of the pressing means20. By passing a current through the pressing means it can be heated.The pressing means 20 is arranged on a first holder means 24 whereas thesubstrate is arranged on a second holder means 25. The device isarranged so that a pressure can be applied between the two holder means.The device also comprises a power source 26, which is intended to beconnected to the pressing means.

FIG. 6 shows two different embodiments of the connection of connectingmeans to a pressing means. FIG. 6 a is a cross sectional view in which apressing means 30 is arranged in contact with a carbon path 31. Thepressing means 30 rests on the carbon path 31 and can slide towards thecarbon path in the direction of the arrow 36. FIG. 6 b shows analternative embodiment in which a pressing means 32 is connected to aconnecting means 33, which comprises a resilient portion 34 that allowsmotion in the direction of the arrow 35. The embodiments shown in FIG. 6are merely exemplifications which can be applied in the area between theconnecting means and the pressing means in one of the embodimentspreviously described.

FIG. 7 shows yet another embodiment of how the pressing means 37 can beconnected to connecting means. In FIG. 7 both the pressing means 37, 38are radially connected from the inner periphery 39 to the outerperiphery 40.

The above embodiments are only to be understood as examples. It is, ofcourse, conceivable to vary the embodiments described in a number ofways within the scope of the claims.

It is not, for instance, necessary to transfer only one pattern to thesubstrate. It is feasible to arrange a layer and a pressing means oneach side of the substrate.

1. A method for transferring at least one pattern in the form of astructure from a pressing means to a deformable layer which is arrangedon a planar surface of a substrate, said method comprising the steps of:connecting a power source over the pressing means, arranging thepressing means in contact with the layer, the pattern facing the layer,operating the power source so that a current is passed through thepressing means, which thereby is heated and indirectly heats the layer,and pressing the pressing means against the layer so that the pattern istransferred to the layer, wherein said power source has at least onecontacting surface connected to a contacting surface of said pressingmeans, said contacting surface of said pressing means having a shape andorientation similar to the contacting surface of said power source,thereby giving a substantially homogeneous current density in saidpressing means.
 2. (canceled)
 3. (canceled)
 4. The method according toclaim 1, wherein the pressing means has an outer periphery and a holewhich defines an inner periphery, and the power source is connectedbetween the inner periphery and the outer periphery.
 5. The methodaccording to claim 4, wherein the power source is connected with the aidof two connecting means, which each extend in the radial direction ofthe pressing means.
 6. The method according to claim 1, wherein the stepof connecting the pressing means to a power source comprises the stepsof: arranging the pressing means in a recess in an electricallyconducting holder means which has a rectangular outer shape, andconnecting the holder means to the power source, wherein the pressingmeans is brought in electrical contact with the holder means along itsentire periphery, thereby giving the combination of holder means andpressing means the same electrical properties as a rectangular plate. 7.A device for transferring at least one pattern in the form of astructure from a pressing means to a deformable layer which is arrangedon a planar surface of a plate-shaped substrate, comprising a firstholder means, and a second holder means for receiving the substrate andthe pressing means, respectively, the device being arranged to apply apressure between the first holder means and the second holder means,wherein said device further comprises: a power source for heating thepressing means, and electrical connecting means for connecting thepressing means to the power source, wherein said power source'sconnecting means has contacting surfaces connected with contactingsurfaces of said pressure means, said contacting surfaces of saidpressure means having a shape and orientation similar to said powersource's connecting means, giving a substantially homogeneous currentdensity in said pressure means.
 8. A device as claimed in claim 7,wherein the pressing means has an inner periphery and an outerperiphery, and the power source is connected between the inner peripheryand the outer periphery.
 9. A device as claimed in claim 8, wherein thethickness of the pressing means decreases with an increasing distancefrom the inner periphery.
 10. A device as claimed in claim 7, whereinthe first holder means comprises a rectangular portion with a recesswhich is formed to receive the pressing means, which portion isconnected on two opposed sides to the electrical connecting means andhas the same resistivity as the substrate and which portion togetherwith the pressing means forms a unit with the same electrical propertiesas a rectangular plate without a recess.
 11. A device as claimed inclaim 7, wherein the pressing means is resiliently connected to thepower source.
 12. A device as claimed in claim 7, wherein the pressingmeans is in moving contact with the connecting means to enable thepressing means to slide in relation to the connecting means.